Special Issue on Air Pollution and its Impact in South and Southeast Asia (III)

Aditi Majumdar1, Dhrubajyoti Samanta  2, Reshmi Das  This email address is being protected from spambots. You need JavaScript enabled to view it.1 

1 School of Environmental Studies, Jadavpur University, Kolkata 700032, India
2 Earth Observatory of Singapore, Nanyang Technological University, Singapore 639798, Singapore

Received: January 29, 2022
Revised: April 12, 2022
Accepted: May 18, 2022

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Download Citation: ||https://doi.org/10.4209/aaqr.220019  

Cite this article:

Majumdar, A., Samanta, D., Das, R. (2022). Chemical Characteristics and Trends of Indian Summer Monsoon Rainfall: A Review. Aerosol Air Qual. Res. 22, 220019. https://doi.org/10.4209/aaqr.220019


  • Trends of major ion composition of rainwater across six homogeneous ISM regions.
  • Acid rain events are more frequent in Peninsular region.
  • Ca2+ is the most potent and abundant neutralizing species over all the regions.
  • Rainwater chemistry has higher ionic composition during El Niño.


The Indian summer monsoon (ISM) regulates the pace of life for billions of people in the Indian subcontinent by driving the agriculture and Gross Domestic Product of the region. The chemical composition of ISM is influenced by pollutant type, meteorology, and topography. As a result, the chemical makeup of rainwater varies greatly across places. The current review article highlights the variations and trends of the principal chemical constituents of rainwater (Na+, K+, Ca2+, Mg2+, NH4+, NO3, SO42–, and Cl) across six homogeneous Indian monsoon regions: Central Northeast, Hilly, Northwest, Northeast, Peninsular and West Central region. Average rainwater pH ranged from 5.31 to 6.70 in these six regions. The incidence of acidic rain events at three separate locations in the Peninsular region suggests a significant impact of anthropogenic emissions. The chemical composition of rainwater in all these regions varied considerably and seemed to form a regional pattern. The majority of the ions in rainwater were highest in the Northwest while lowest in the Peninsular region. Cl had a significant correlation with Na+ and NH4+ in the Hilly region, and with Na+ and Mg2+ in the West Central region suggesting it is sourced from both marine and anthropogenic sources. The soil Enrichment Factor relative to Ca2+ demonstrated that soil has a significant effect on rainwater composition. Ca2+ was determined to be the most abundant neutralizing ion in all the regions. Furthermore, the synthesis of rainwater chemistry reveals a strong relationship with dominant interannual climate variability El Niño Southern Oscillation with significantly higher concentrations of Na+, K+, Ca2+, Cl, and SO4 in rainwater during El Niño year compared to La Niña year.

Keywords: Rainwater, Major ions, Enrichment factor, Trend analysis, ENSO

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